The present invention relates to clutches, and more particularly to clutches used with outdoor power equipment, such as a self-propelled, walk-behind mower.
Mechanical clutches are well known devices employed for selectively coupling a driving member with a driven member. Typically, such members rotate coaxially relative to one another. A wide variety of machinery utilize clutch devices, for example, outdoor power equipment, such as lawn equipment. More specifically, a certain class of lawn equipment commonly known as self-propelled, walk-behind mowers is known to use some form of clutch to transfer power from a main power source, frequently an internal combustion engine, to one or more of the mower wheels so as to allow the mower to move over grass and/or other vegetation to be mowed. Previous mowers in this class have been known to operate awkwardly and somewhat hazardously because their clutching means were designed to rapidly engage and to remain activated until the mower operator consciously and decisively deactivates the clutching means. This activation usually occurs by manipulating a clutch control device, the mowers almost instantaneously achieve a driven state upon clutch engagement and thereafter, they remain in a driven state until the operator manually disengages the clutching means via the clutch control device.
Instantaneous engagement of the clutch results in xe2x80x9cjack-rabbitxe2x80x9d starts and a frequent need either to manually disengage the clutch or to apply extra muscle to maneuver the mower about the area to be mowed. Newer clutching means, known as freewheeling bi-directional clutches, are suitable for operatively coupling and decoupling a driven member with a driving member without the usual manual intervention. An example of one of these freewheeling bi-directional clutches is provided in U.S. Pat. No. 4,909,365 issued to Tillotson, et al. (hereinafter the xe2x80x9c""365 Tillotson patentxe2x80x9d or more simply xe2x80x9cTillotsonxe2x80x9d).
The clutch taught by the ""365 Tillotson patent is a friction-actuated clutch having among its critical design features, an internal, preferably metallic, key and a friction disk preferably made of plastic. The friction disk cooperatively engages the key so as to cause it to assume an extended, or cocked, state when a gearbox output drive shaft rotates in a particular direction and a retracted, or un-cocked, state when the gearbox output drive shaft ceases to rotate.
The key is configured to include a wedge portion and a tang portion extending from the wedge portion. The tang portion at all times floatingly resides fully in a tang relief formed by the friction disk. The wedge portion, when it is in its retracted or un-cocked state floatingly resides fully within a first axial keyway formed by the gearbox output drive shaft. The wedge portion, when it is in its extended or cocked state, floatingly resides partly in the first keyway and partly in one of a plurality of second axial passageways formed by a drive pinion that is also a component of the clutch design taught by the ""365 Tillotson patent.
Another operative component of the clutch disclosed by the ""365 Tillotson patent is a coiled thrust spring. The thrust spring along with the drive pinion and the friction disk are concentrically applied to the end portion of the output drive shaft that forms the first keyway and that projects outwardly from an orifice provided through a pivot housing. The end portion of the output drive shaft is provided with two axially spaced grooves on its outer surface. When applied to the output drive shaft, the friction disk, the drive pinion, the key and the thrust spring all lie between the two grooves. Both of the grooves are designed to receive a retainer clip. A first one of the grooves is situated on the output drive shaft so that it is adjacent to the portion of an outboard face of the pivot housing, which surrounds the orifice from which the gearbox output drive shaft protrudes. When fitted in the groove, the inboard face of the retainer clip abuts against the face portion of the housing and resists axial motion of the shaft relative to the housing.
A second of the grooves is positioned nearer to the end of the output drive shaft, and when the second retainer ring is fitted into the second groove, the thrust spring is compressed and an axially directed spring force, acting first through the drive pinion and then through the friction disk, presses the inboard face of the friction disk against the outboard face of the pivot housing, creating a state of static friction between the two surfaces. In a like manner, a portion of the inboard face of the drive pinion is pressed against the outboard face of the friction disk, also creating a state of static friction between these two surfaces. Because the inboard face of the drive pinion is outwardly bowed or crowned, and contacts the friction disk at a smaller radius than the radius at which the friction disk contacts the housing, a lesser amount of force is needed to cause motion of the drive pinion relative to the friction disk than is needed to cause motion of the friction disk relative to the housing. Consequently, when the drive shaft does not rotate, it is possible to maintain the key in a retracted or un-cocked state and for the pinion to freewheel relative to the drive shaft, the friction disk, and the housing.
Alternatively, when the drive shaft, and hence the first axial keyway formed thereby, is caused to begin rotating in a first direction relative to the housing, which direction is also toward the leading edge of the wedge portion of the key, friction force exerted by the friction drag disk against the tang portion of the key tends to rock the key so that a leading edge of the wedge portion become positively engaged with one of the plurality of second keyways provided in the drive pinion. When this happens, drive torque is transferred from the gearbox output shaft to the drive pinion and from the drive pinion to a traction drive wheel of the power implement. The result is self-propelled movement of the housing relative to the underlying ground surface.
When the output drive shaft ceases to rotate in the just described manner, the key is returned to its retracted or un-cocked state. Return of the key to the retracted state is accomplished by allowing the drive pinion to turn a short distance relative to the output drive shaft and to cause the key to be xe2x80x9cwiped downxe2x80x9d into the first axial keyway and to thereafter freewheel in either a clockwise or counterclockwise direction without re-cocking the key, until the drive shaft is again caused to rotate toward the leading edge of the wedge portion. During freewheeling, only the pinion gear rotates relative to the drive shaft. The friction disk remains stationary relative to the housing, the drive shaft and the drive pinion.
In view of the foregoing, it should be evident that the clutch design taught by the ""365 Tillotson patent overcomes drawbacks associated with earlier clutch designs. The clutch design of the present invention also remedies the shortcomings of earlier clutches; however, it does so in a markedly different way than taught by the ""365 Tillotson patent. A way that does not require the existence of friction differentials between a housing and a friction disk and between a drive pinion and the friction disk. The friction differentials in the present invention arise through the action of a thrust spring pressing the components axially together and through component features that result in different contact area sizes.
The present invention is directed to a powered implement, such as a self-propelled, walk-behind lawn mower provided with at least one traction drive wheel assembly including a bi-directional freewheeling clutch suitable for operatively coupling a driven member with a driving member. The driven member and the driving member are configured to rotate relative to a mower housing, the bi-directional freewheeling clutch comprising a pawl having a base portion and an arm portion extending from the base portion, and further the pawl having a neutral un-extended state, and an engaged extended state relative to the driving member. A drive disk concentric to the driving member and adapted to be engaged by the pawl. A friction seal concentric to the driving member and adapted to receive the drive disk. A drive retainer concentric to the driving member and adapted to receive the pawl and the biasing means. A biasing means engaged with the pawl and the drive retainer and a pinion wheel concentric to the driving member and adapted to receive the drive retainer. The pinion wheel is provided with a plurality of gear teeth that operatively mesh with a plurality of similarly designed gear teeth provided on a traction drive wheel.
When an output drive shaft operatively connected to a gearbox included on the mower is caused to rotate in a first rotational direction, the pawl, which includes a tang portion, is caused, through engagement with the drive disk, to assume the engaged, extended state and to thereby engage one of a plurality of projections provided in a recess portion of the pinion wheel. Engagement of the tang with one of the plurality of projections causes drive torque to be transferred from the drive shaft, through the driver retainer and the pawl to the pinion wheel. Drive torque is then transferred to the traction drive wheel and the mower is caused to move relative to an underlying ground surface through contact between the traction drive wheel and the ground through the plurality of gear teeth provided on the pinion wheel that mesh with the plurality of teeth provided on the traction drive wheel.
When the output drive shaft ceases to be driven by the gearbox and thus ceases to rotate in the first rotational direction, the traction drive wheel and the pinion wheel are free to continue rotating in the first rotational direction, and if they continue to do so through the effect of inertia and/or force applied by a human operator of the mower, the pawl disengages from the pinion wheel and through the action of a torsion spring connected to both the pawl and the drive retainer the pawl assumes the neutral, un-extended state. With the pawl in the neutral, un-extended state, both the traction wheel and the pinion wheel are free to rotate either in the first rotational direction or in an opposite second rotational direction, while the drive retainer and the drive shaft do not rotate.
Accordingly, it is an object of the present invention to provide a powered implement such as a self-propelled, walk-behind lawn mower, including at least one freewheeling, bi-directional clutch for operatively coupling and de-coupling a driven member without the need for manual de-clutching and further without the need for the existence of frictional differentials between clutch members, the frictional differentials being induced through axial pressing together of clutch components by a thrust spring and through different sizes of frictional contact areas.
This and other objects of the present invention will be made clear by reference to the detailed drawings and written description of the invention that are hereinafter provided.